bl_info = {
    "name": "Side Shelf",
    "author": "Jesse Doyle",
    "blender": (3, 2, 0),
    "description": "E Shelf on the right side N panel",
    "category": "Side Tabs"
}

import os
import bpy
import bpy.utils.previews
from os import listdir
from os.path import isfile, join


class NPanel(bpy.types.Panel):
    """Creates a Panel in the 3D view Tools panel"""
    bl_idname = "TEST_PT_Panel"
    bl_label = "Test"
    bl_category = "Shelf"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"
    bl_context = "objectmode"

    def draw(self, context):

        layout = self.layout
        pcoll = preview_collections["main"]

        row = layout.row()
        triangle_icon = pcoll["triangle"]
        square_icon = pcoll["square"]
        row.scale_x = 10.0
        row.scale_y = 8.0

        row.operator("mesh.primitive_cube_add", text="", icon_value=triangle_icon.icon_id)
        row.operator("mesh.primitive_uv_sphere_add", text="", icon_value=square_icon.icon_id,scale=10)


# global variable to store icons in
# custom_icons = None

# def register():
#     global custom_icons
#     custom_icons = bpy.utils.previews.new()

#     for z in list_raw:
#         custom_icons.load(z[:-4], os.path.join(directory, z), 'IMAGE')

#     bpy.utils.register_class(Panel)

# def unregister():
#     global custom_icons
#     bpy.utils.previews.remove(custom_icons)

preview_collections = {}


def register():

    # Note that preview collections returned by bpy.utils.previews
    # are regular py objects - you can use them to store custom data.
    pcoll = bpy.utils.previews.new()

    # path to the folder where the icon is
    # the path is calculated relative to this py file inside the addon folder

    directory = os.path.join(os.path.dirname(__file__), "Data", "icons")
    list_raw = []
    onlyfiles = [f for f in listdir(directory) if isfile(join(directory, f))]

    for f in onlyfiles:
        if f[-4:] == ".png":
            list_raw.append(f)

    for z in list_raw:

        # load a preview thumbnail of a file and store in the previews collection
        pcoll.load(z[:-4], os.path.join(directory, z), 'IMAGE')

    preview_collections["main"] = pcoll

    bpy.utils.register_class(NPanel)


def unregister():

    for pcoll in preview_collections.values():
        bpy.utils.previews.remove(pcoll)
    preview_collections.clear()

    bpy.utils.unregister_class(NPanel)


if __name__ == "__main__":
    register()